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  1. #1
    cmgww's Avatar
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    It's ALIVE!!! ALIVE!!!! My 1390

    Finally got my ski on the water again this past weekend. Thanks to LT1GMC for the wrench work..he's a great GP mechanic and better father.

    So this baby screams!! Right now we are waiting on the prop, so for the time being we are running a 14/? prop, and the PET tach has me at 7300. I know that is a little shallow for this engine, I want top RPMs in the 7050-7150 range. Plus we haven't dialed in the carbs; that is useless without the right prop...running 155 high speed jets to ensure no seizures, but with EZ tune screws we can turn them down a bit (was WAY rich this weekend and I went through gas like an old 1200 circa 1999 I know the 1390 will eat more gas, but this was ridiculous.

    Anyway...I have a friend with an RXT and walked away from 40mph on....first kill! It wasn't from idle, b/c I knew the prop on there was cavitating big time, so we ran at maybe 15-20 or so. We were even off the line, then I took him by a few...

    Top GPS was 76 but sustained was only 73.5...I know some tweaks will help. I am running the big pump and 1200 grate b/c I run in less than perfect water. This motor has a ton more in it, I can feel it from around 30-60. Thanks to Lowell for suggesting the fuel pressure gauge. It's reading 6.5 at WOT and around 3 at mid to 3/4 throttle...Nice to have. Dual fuel pumps help too.

    Side note: some jackass on an older RXP was running our choppy section of the lake at WOT, then slowed. I pulled along side him where the lake gets smooth...no race. I lost patience and took off. But he raced my brother (GP1200 with 150psi head, stuffers, grate/plate, FAs, basically a Stage 1 GPR) and LOST. Dude then u turns and heads back up the lake at full speed! Weenie...He knew I would kill him in flat water...I need to quiet the exhaust b/c it gives me away.

    Summary: My ski has a TON of speed left in it. The prop will solve a lot of it, and shimming the tabs (at 70+ even a pontoon wake causes loss of hookup).
    Stay tuned for the REAL SPEED numbers...it's not going to be a glass queen b/c I plan on dusting off RXP 260Xs in moderate chop....
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  2. #2
    cmgww's Avatar
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    My brother's GPR is the blue one in the pic....to hit 70+ with his mods is very well done.

  3. #3

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    Your jetting of 155 on the mains seams to be way rich if you are using oem carbs and running a single pipe ski. With a 1390 and oem carbs with after market air filters I use 140-145 mains @ 1-3/4 to 2-1/4 turns out on the screw. Tommy Jordan

  4. #4
    cmgww's Avatar
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    Quote Originally Posted by 2fast4u View Post
    Your jetting of 155 on the mains seams to be way rich if you are using oem carbs and running a single pipe ski. With a 1390 and oem carbs with after market air filters I use 140-145 mains @ 1-3/4 to 2-1/4 turns out on the screw. Tommy Jordan
    We thought 145s would be fine, right up until it seized and burnt up #1 and 2....So we went bigger to prevent the same thing from happening again. And we added a 2nd fuel pump to maintain pressure. But after the rebuild, my dad thinks it might have been the fuel pump and not the jet sizing that caused the seizure, from reading on here what others with similar 1390s have. Thus the 2nd pump. So this winter we might back it down, but for now it's staying at 155 and I'll just pay for the gas. b/c it's running great and summer up here is too damn short to tear it down again to put in smaller jets. we can back down on the screws for now, that will help a bit, then change out the jets this fall/winter if we're still running rich....

  5. #5
    cmgww's Avatar
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    UPDATE: Finally got the prop that's meant to go with the engine on the boat. Dynafly setback, 14/25 (I think?) Currently having the plate grinded a bit to change the angle for better rough water handling. Carbs still way rich, but I didn't want to touch the T screws without my Dad around. I guess I need to have him teach me how to adjust the high speeds on the fly (got the general idea, but want the specifics).

    Funny story. Wanted to ride this last weekend, wife's sister getting married so a day on lake was a part of the party....My ride plate (R&D extended) not done, Pops threw on a stock plate just for the weekend so I could at least ride with friends/family. Not to mention he shimmed the tabs down a bit. Anyway, I get on it...good hookup! Gets up to speed nicely, then I go to turn and about get thrown off b/c it's hooking so hard! I was used to the "loose" setup...I trim it all the way up and she's still carving like she's on rails...Obviously the stock plate and tabs setup wasn't going to work...but hey it was just to make it rideable for this weekend. Also lost some big time speed due to the stock plate, but no big deal. RPMs are down from seat-of-pants perspective, and she kills from 30-60. Some dufus on the lake pulled up as I was cruising; he was on an older Sea-Doo GPi (yellow/blue)...I was going maybe 50, let him get a lead, then boom...blew by him like he was standing still! Nice!!

    Just an update. Obviously the R&D angled plate and carb fine tuning will get this ski to mid to high 70s in the right temps. I do love the fact that I never lost the hookup even in mild chop. Balance that needs to be maintained.

  6. #6

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    I hope you are up past 77 pretty soon, or I am gonna stay #1. Just so you know, blue is a faster color than silver.

  7. #7
    Julian's Avatar
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    Welcome to the wonderful world of 1390cc

    This is the real deal!
    just bring lots of fuel!

  8. #8
    cmgww's Avatar
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    Quote Originally Posted by LT1GMC View Post
    I hope you are up past 77 pretty soon, or I am gonna stay #1. Just so you know, blue is a faster color than silver.
    Pretty sure you used 1/2 inch shims on the tabs to slow me down...lol. Should they stick down below the hull like they are??

  9. #9
    cmgww's Avatar
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    Got a reading of 75.1 a few weeks back at 6700 RPMs...on a GPS I bought that seems to be reading 1 MPH slow consistent with my father's Garmin. Pulled the prop and it is a 16/25...that is steep. We are trying a 14/23 to bring the revs up to around 7200 or a bit higher. Loading the engine with too steep a prop is bad. And we tried tuning the carbs including closing the high speeds all the way, with no difference in revs, so the prop is the next step. Compression is fine....this weekend it is supposed to be low 70s with low humidity, so if all goes well we should see 77-78 at least (ride plate has been angled too) Shims got rid of the dreaded high speed bounce. Stay tuned.

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